Understanding kleptoplasty in Sacoglossa (Heterobranchia, Gastropoda) - a cellular histochemical and genomic approach

Sacoglossa是一种神秘的异枝类群，一些成员能够从藻类食物中吸收叶绿体（cps），并且在不额外喂食的情况下存活数周甚至数月。最近的转录组分析拒绝了旧的假设，该假设认为藻类核基因组和鼻涕虫核基因组之间的水平基因转移是这种相互作用的基础。因此，cps的保留不能通过基因转移的遗传支持来解释。因此，新的假设必须转向cps和鼻涕虫的相互作用和特定属性。在过去几年中，我们对Sacoglossa的了解有了相当大的增长，包括系统发育关系、食物特异性、蛞蝓行为和光合能力方面的信息。这一信息解释了提高cps维持和鼻涕虫存活的几个因素，然而只有很少的研究涉及细胞水平的特性。以前的结果（包括我们自己的结果）表明，只有少数叶绿体类型的特定存活率，cps的特定存活率取决于饥饿和食物供应，以及鼻涕虫的个体发生阶段。本项目旨在阐明cp在细胞水平上的整合过程，并探讨cps在鼻涕虫消化腺细胞中的作用，特别是它们作为一种长期能量储存装置的贡献，并能在一定时间内增加营养价值。本研究将利用超微结构，免疫组织化学和共聚焦激光显微镜方法来确定每个合并的cp一旦摄入的路径。定量方法（形态计量学、定量实时PCR和生化分析）将有助于阐明cps作为营养仓库的贡献。基因表达的研究将有助于了解蛞蝓在不同饥饿阶段的生理和遗传特性。我们重点研究了姐妹类群，Elysia timida和E. cornigera，它们都以髋臼为食。野田菊可以保留几个月的功能cps，而野田菊只能保留几个星期的功能cps

Sacoglossa is an enigmatic heterobranch group, well known for some members ability to incorporate chloroplasts (cps) from their algal food and to survive weeks and months without additionally feeding. Recent transcriptome analyses reject old hypotheses, which suggested a horizontal gene transfer between the algal nuclear genome and the slugs nuclear genome as the basis for this interaction. Thus, the retention of cps cannot be explained by genetic support via gene transfer. New hypotheses must therefore shift to interactions and specific properties of cps and slugs. Our knowledge on Sacoglossa has increased considerably in the last years, including information on phylogenetic relationships, on food specificity, slug behaviour and photosynthetic capability. This information explains several factors that enhance cps maintenance and slugs survival, however only few studies have dealt with the properties on cellular level. Former results (including our own) indicate a specific survival of only few chloroplast types, a time specific survival of cps dependant on starvation and food availability, as well as slugs ontogenetic phase. This project aims to clarify the cp incorporation processon cellular level and explore the role of the cps in the slugs digestive gland cells, especially concerning their contribution as a long-term energetic storage device with the ability to increase nutritional value over a certain period of time. This investigation will utilize ultrastructural, immunohistochemical and confocal laser microscopical methods to determine the path each incorporated cp takes once ingested. Quantitative methods (morphometry, quantitative real time PCR (qPCR) and biochemical analyses) will help to elucidate the contribution of the cps as nutrional depots. Study of gene expression will help to understand physiological and genetic properties of the slugs during various starvation phases. We focus on sister-taxa, Elysia timida and E. cornigera, both of which feed on Acetabularia. E. timida can retain functional cps for months whereas E. cornigera can only retain cps for a few weeks